The present invention relates to an actuator device, comprising piezoelectric elements that are deformed by the application of a voltage to a piezoelectric layer. In particular, the present invention relates to a liquid ejection head wherein a part of a pressure generating chamber, which communicates with a nozzle orifice through which liquid droplets are ejected, is formed of a vibration plate, on the surface of which piezoelectric elements are disposed, so that liquid droplets are ejected when the piezoelectric elements are deformed. The present invention also relates to a method of inspecting such an actuator device and such a liquid ejection head.
As one example of the liquid ejection head, there is an ink jet recording head wherein a part of a pressure generating chamber, which communicates with a nozzle orifice through which ink droplets are ejected, is formed of a vibration plate, on the surface of which an actuator device comprising piezoelectric elements of flexure vibration mode are disposed, so that ink droplets are ejected when the piezoelectric elements are deformed.
For such an ink jet recording apparatus, the piezoelectric elements can be mounted using a relatively simple process, whereby either a green sheet composed of a piezoelectric material and corresponding in shape to that of the pressure generating chamber, is glued to the vibration plate, or coated on the vibration plate by printing, and the resultant structure is baked. With such an apparatus, however, high frequency ejection is difficult, and in order to resolve this problem, as is disclosed in Japanese Patent Publication No. 2-289352A (see FIG. 5, and page 6, line 9 of the lower left column through line 14 of the lower right column), a two-layer piezoelectric member is employed and the deformed amount of the piezoelectric element is increased.
Such an ink jet recording head, comprising multilayer, laminated piezoelectric elements, enables relatively high frequency ink ejection. However, since when piezoelectric layers are used to form a piezoelectric element, thickness errors occur and the characteristics of the layers are not uniform; and when printing is used for coating the piezoelectric layers, thickness errors, especially, tend to be increased. Therefore, before a piezoelectric element is formed, the electrostatic capacities of the piezoelectric layers are measured, to identify the relevant characteristics, and in accordance with the characteristics, an appropriate drive waveform is selected to drive the piezoelectric element.
However, for an ink jet recording head comprising piezoelectric elements having the multi-layer structure, since the lower common electrode and the upper common electrode of each piezoelectric element are electrically connected, even when the electrostatic capacities of the piezoelectric layers are to be measured after the manufacturing process has been completed, only the overall electrostatic capacity of the piezoelectric layers can be measured. As a result, the characteristics of the piezoelectric element can not be accurately identified.
Namely, even for piezoelectric elements for which the piezoelectric layers have the same overall electrostatic capacity, the deformation characteristics differ depending on the ratio of the thickness of the lower piezoelectric layer to the thickness of the upper piezoelectric layer. Therefore, the characteristics of the piezoelectric element can not be accurately identified merely by referring to the overall electrostatic capacity of the piezoelectric layers.
These problems also apply for an actuator device that is mounted on a liquid ejection head, such as a liquid crystal ejection head or a coloring material ejection head.